The present invention relates ultrasonic flow meter devices and methods thereof. The present invention also relates to ultrasonic flow meter devices utilized in semiconductor fabrication processes, including CMP (Chemical Mechanical Polishing) operations.
Ultrasonic flow meters have many advantages over other methods of determining flow rates. Ultrasonic flow meters can continuously measure the flow rate, while other methods generally measure average flow rates. In addition, ultrasonic flow meters are obstructionless and work with non-conductive fluids.
Ultrasonic flow meters are generally configured, such that a generated ultrasonic wave is caused to propagate through a fluid flowing through a tubular path of the ultrasonic flow meter. In typical ultrasonic flow meters, the velocity of the fluid flowing through the tubular path is determined on the basis of the difference between the rate of propagation of the ultrasonic wave that propagates from an upstream to a downstream and that, which propagates from the downstream to the upstream.
A typical prior art flow meter includes a conduit through which a fluid flows and a pair of ultrasonic transducers disposed in the conduit along a line, which is inclined by a predetermined angle with respect to a fluid flowing direction. In the operation, initially, an ultrasonic wave is emitted from the ultrasonic transducer disposed on the upstream side with respect to the flowing direction, toward the downstream side, and is received by the ultrasonic transducer on the downstream side. Then the propagation time from the emission to the reception of the ultrasonic wave is determined. Subsequently, an ultrasonic wave can be emitted from the ultrasonic transducer disposed on the downstream side with respect to the flowing direction, toward the upstream side, and is received by the ultrasonic transducer on the upstream side, and the propagation time from the emission to the reception of the ultrasonic wave is determined. Substituting the two propagation times into a well-known equation yields the velocity of the fluid, with which the rate of flow may be determined.
Ultrasonic flow meters are thus precision-sensitive devices utilized to measure flow rates. Such devices, however, have a number of disadvantages when applied to particular operations requiring precision measurements. These disadvantages are particularly noticeable in CMP (Chemical Mechanical Polishing) operations utilized in semiconductor device fabrication environments. One of the primary disadvantages of prior art ultrasonic flow meters in CMP operations involves the formation of bubbles within a slurry flow. In such scenarios, the ultrasonic wave in the flow is typically scattered by such bubbles, resulting in poor and inaccurate measurements. Thus, it is necessary to avoid bubbles passing through ultrasonic flow meters utilized in semiconductor device CMP operations in order to avoid influencing the flow rate.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is therefore one aspect of the present invention to provide an improved ultrasonic flow meter and methods thereof.
It is therefore another aspect of the present invention to provide an improved ultrasonic flow meter method and methods thereof for use in semiconductor fabrication operations.
It is still another aspect of the present invention to provide an improved ultrasonic flow meter method and methods thereof for use in Chemical Mechanical Polishing (CMP) operations.
It is yet another aspect of the present invention to provide an improved ultrasonic flow meter method and methods thereof for limiting measurement errors derived from ultrasonic flow meters utilized in CMP operations.
The above and other aspects of the present invention can thus be achieved as is now described. A method and apparatus for preventing flow rate errors derived from an ultrasonic flow meter utilized in semiconductor fabrication operations are disclosed herein. The ultrasonic flow meter is generally configured to include an extension chamber connected to a thin branch tube of the ultrasonic flow meter. A venturi tube can be positioned at an outflow location of the ultrasonic flow meter, such that the thin branch tube is broached into the venturi tube, wherein bubbles contained in a slurry flow are forced directly into the outflow location to thereby prevent inaccurate flow measurements derived from the ultrasonic flow meter. The extension chamber may be configured to reduce an inflow velocity associated with the slurry slow and ensure that the bubbles with not drift with the slurry flow.
Additionally, a diameter of the branch tube may be configured such that the diameter is much smaller than a diameter associated with an inflow and/or outflow tube of the ultrasonic flow meter. A first terminal of the thin branch tube may be connected to the venturi tube to establish an outflow tube. Additionally, the ultrasonic flow meter may be configured such that a differential pressure exists form the extension chamber toward an outflow tube of the ultrasonic flow meter. The slurry flows into an outlet tube of the ultrasonic flow meter and does not pass through the ultrasonic flow meter. Such an ultrasonic flow meter may be adapted for use in Chemical Mechanical Polishing (CMP) operations. The bubbles may comprise a plurality of mini-bubbles.